Biology 111B

Study Questions 17: Genetic control of development
Answers

1. What does the term "differentiation" mean?

 Differentiation is the process by which cells of a multicellular organism become different from one another and specialized for a particular function. This is caused by differences in which genes are being expressed in the different cell types.

2. What are three broad categories of genes that function in differentiation? In what order do they act in Drosophila?

In order, the three categories are:

maternal effect or egg polarity genes
segmentation genes
homeotic genes

3. Why do we care about how an insect like Drosophila develops?
We care about development in Drosophila because many of the genes that control Drosophila are conserved over evolution and function in mammals (including humans) as well.

4. What is induction? Give an example of how it works.
Induction is the process by which cells send chemical signals to adjacent cells and, through those signals, control the further development of those adjacent cells. An example is in the development of the eye, where, in the anterior end of the neural tube, the optic vesicle induces the adjacent ectoderm cells to make an eye lens "placode." The production of the placode reciprocally induces the optic vesicle to form the optic cup, which in turn, induces the lens placode to form a cornea and lens.

5. The establishment of a dorsal-ventral axis in a developing embryo is a crucial aspect of… (only one correct answer)

a. transcriptional regulation

b. pattern formation

c. cell division

d. induction

6. Cell differentiation involves… (circle all correct answers)

a. the action of tissue specific transcription factors

b. the action of maternal proteins in the egg/embryo

c. the selective loss of certain genes from the DNA

d. the action of maternal DNA in the egg/embryo

 

7. Select the correct statement(s) concerning the bicoid gene and its role in Drosophila development. (only one correct answer)

a. Defects in the gene result in embryos with heads at both ends.

b. Maternal bicoid RNA is deposited within the unfertilized egg and translated only after fertilization.

c. The bicoid protein is made by the mother.

d. The production of bicoid protein and its diffusion to adjacent cells demonstrates induction.

8. Homeotic genes… (only one correct answer)

a. encode transcription factors that control the expression of genes responsible for initiating specific anatomical structures

b. are found only in Drosophila and other insects

c. specify the anterior-posterior axis for the embryo

d. create the basic segments of the embryo

9. How does the term "developmental cascade" describe the actions of transcription factors during development?
A developmental cascade describes the situation when a transcription factor activates the production of another (or several other) transcription factors, which in turn, activate other transcription factors. Eventually, this cascade results in differentiation of the cells under its control.

10. Given the function of the bicoid gene product, if large amounts of bicoid protein were injected into several areas of a Drosophila egg, what would be the outcome?
When this experiment was actually done, anterior structures developed at each injection site.